Account Collections Issue

I have a collections agency who put a flag on my credit which I need to pay before getting a mortgage. Best I can tell it is from Telus wireline which was my home account number from 2019. I am a long time Telus mobility customer to this date and have not been told of any balance owing for this account from Telus.  I think this process of getting collections involved is critically impacting families who need to have housing security. The issue is Telus never contacted directly for amount of around $300 that has now several years later skyrocketed to $1700. How can one expect to continue with a company for mobility services who practices in this way?!